1. Field of Invention
The present invention relates generally to a steering system for a vehicle and more particularly to steering control with variable damper assistance for a steer-by-wire steering system.
2. Discussion of Related Art
In a steer-by-wire system, the mechanical linkage between steering wheel and road wheels has been eliminated. The steering wheel angle command signal (designated as driver input) is translated to a road wheel angle by using electric analog or digital signals.
Even though the mechanical linkage between the steering wheel and the road wheels has been eliminated, a steer-by-wire steering system is expected not only to produce the same functions and steering feel as a conventional mechanically linked steering system, but it is also expected to implement advance steering system features. Such a steering system is disclosed in U.S. patent Ser. No. 09/808,259 the entire content of which is incorporated herein by reference. Requirements for conventional steering functions and advanced steering features such as adjustable steering feel can be implemented by an advanced control system design.
A steer-by-wire control system must satisfy high quality steering requirements and functions, such as a vehicle directional control requirement, a steering wheel to road wheel synchronization requirement, adjustable steering effort functions, stability and adjustable returnability functions, capturing a driver""s intent, and adjustable steering feel functions. On the other hand, the resultant control system structure and control strategy must satisfy closed-loop feedback control system requirements and specifications, such as maintaining stability in the face of uncertainties, rejecting disturbance performance, and quick time response performance.
One aspect of the present invention regards an automotive steering wheel control system having a steering wheel, a magnetorheological damper in communication with the steering wheel and a road wheel control system operably connected to the magnetorheological damper, wherein the magnetorheological damper controls the steering wheel in response to the magnetorheological damper receiving a signal from the road wheel control system.
Another aspect of the present invention regards a steering lock-to-lock apparatus having a steering apparatus, a switch in communication with the steering apparatus and a magnetorheological damper responsive to the switch, wherein when the switch is in a lock state the magnetorheological damper locks the steering apparatus.
Another aspect of the present invention regards a magnetorheological damper control for an automotive steering control system having a motor amplifier receiving a reference signal and generating a motor torque signal, a motor receiving an effective torque signal based on the sum of a magnetorheological torque signal, a driver action torque signal and the motor torque signal. The motor generates a steering wheel rotation based on the effective torque signal. A magnetorheological damper receives an amplified control signal from a magnetorheological amplifier. The magnetorheological amplifier receives a road wheel torque control input signal and generates the amplified control signal based on the road wheel torque control input signal. The magnetorheological damper generates a magnetorhelogical torque based on the magnetorheological torque signal.
Another aspect of the present invention regards a steering wheel control system for a vehicle comprising a first control subsystem having a magnetorheological damper, a steering wheel motor responsive to a controlled input torque signal, wherein the first control subsystem generates a steering wheel torque signal. The steering wheel control system also has a second control subsystem having a position loop compensator, a gain adjustable function element responsive to an output from the position loop compensator, a motor and a motor amplifier that receives an reference signal from the gain adjustable function element and generates a motor torque. The second control subsystem generates a steering wheel angle signal and a third control subsystem has a steering ratio function element and a road wheel control subsystem. The steering ratio function element receives the steering wheel angle signal and generates a road wheel reference angle signal. The road wheel subsystem receives the road wheel reference angle signal and generates a road wheel angle signal.
Another aspect of the present invention regards a method of improving steering feel in an automotive steer-by-wire control system by sensing a steering wheel angle, sensing a road wheel torque, controlling a magnetorheological damper in response to the steering wheel angle and the road wheel torque and controlling steering feel in response to the magnetorheological damper.
Another aspect of the present invention regards a method of locking a steering system by producing a steering apparatus position, controlling a magnetorheological damper in response to the apparatus position and locking the steering apparatus in response to the magnetorheological damper.
All of the above aspects of the present invention provide the advantages of providing an energy efficient adjustable steering feel for the driver while reducing the energy consumption and decreasing the package and cost of the steering system.
Additional embodiments and advantages of the present invention will become apparent from the following description and the appended claims when considered with the accompanying drawing.